ABSTRACT

Males of certain arthropods feed their mates during mating. Nowhere is the diversity of this courtship feeding greater than in the Orthopteran suborder Ensifera, the katydids, weta, and the humped–winged, wood, Jerusalem, mole, cave, camel as well as tree and other true crickets. In this chapter I discuss the origin and current utility of male glandular and body–part donations in the Ensifera. Character analysis shows that the ancestral ensiferan female removed and ate a sperm ampulla (spermatophore) that was positioned externally on her genitalia. This was followed by at least 11 origins of mate feeding, most cases of which involved female feeding on the male contribution during insemination. This sequence of events indicates that male contributions evolved through sexual selection and sexual conflict as meal size increased and prolonged the attachment of the sperm ampulla, thus increasing paternity. The most common type of male contribution in Ensifera – a gelatinous spermatophylax attachment to the sperm ampulla – evolved three times. A spermatophylax is found in virtually all katydid species (Tettigoniidae) and the other four families in the same clade. For the current utility of courtship feeding there is experimental support for different functions in different species: in a humpedwinged cricket (Haglidae), two true crickets (Gryllidae) and two katydids, wing, gland or spermatophylax feeding increases paternity by preventing consumption of the sperm–ampulla. In cases of precopulatory feeding, the meal functions to obtain mates.

ABSTRACT

We review mating–systems theory and conflict theory and apply them to the analysis of intrasexual and intersexual conflicts. We distinguish three types of sexual interaction, persuasive, coercive, and forcing, that are used by members of each sex to gain control over fertilization and reproductive resources, and we discuss the nature of male–male, female–female and intersexual interactions with respect to these types of behavior. The mating sequence from pair formation to the end of parental care provides the context for analyzing sexual conflict and confluence of interest; events during any given stage in the sequence may affect the dynamics of other events. We suggest that three main sets of variables influence the evolution of mating systems: (1) resource and mate distributions; (2) the presence and extent of transferrable genetic and material benefits; and (3) the degree of control exerted by each sex over events at different stages in the mating sequence. The former two sets of variables are more or less predictable from ecology, demography and life–history adaptations not directly related to mating behavior; the latter is intimately related to the first two, but should often be unpredictable owing to the idiosyncracies of lineage–specific events.

INTRODUCTION

Insects and arachnids display a diversity of reproductive strategies unparalleled among animals; this diversity has put research on these creatures at the forefront of the study of animal mating systems (Blum and Blum 1979; Thornhill and Alcock 1983; Gwynne and Morris 1983; Smith 1984).

ABSTRACT

Cricket reproduction has been studied at both the proximate level, focussing on the neurophysiological mechanisms involved in the transmission and reception of calling song, and the ultimate level, focussing on how selection might have acted on male and female behavior. Although mating patterns are diverse, most crickets do not have sub – stantial male contributions to females or offspring, making female choice a common mode of sexual selection. Males are extremely aggressive, with possession of a burrow and large body size tending to increase the likelihood of success in male interactions. Population density is an important determinant of male spacing, calling, and mating success.

Although several studies have established the existence of non–random mating, the song attributes that females presumably use in making long–distance discriminations are not always clear. Diel patterning of calling is likewise little studied. Non–callers may represent, not a distinct class of males pursuing an alternative mating strategy, but males responding opportunistically to changes in population density. Several cricket species appear to have responded to selection pressure by phonotactic parasitoids.

Female crickets commonly mate more than once; females benefit in several ways from having larger sperm reserves. Field studies comparing traits of males found paired with females with those of calling males show a consistent relationship between pairing success and male age. Age seems to be used as an indirect indication of male quality. Courtship behavior may also indicate variation in male quality to females.

ABSTRACT

We provide a general overview of lek behavior in insects. Initially, we draw a distinction between substrate–based and aerial (swarming) male mating aggregations. In general, males in substrate–based groups defend territories, wait for arriving females, and perform courtship prior to mating. By contrast, males in swarms typically exhibit no intrasexual aggression before female arrivals and grasp approaching females for immediate mating without courtship. Also, compared with swarms, substrate–based aggregations tend to be small, and males are more likely to produce long–range signals to attract females. We examine the relative importance of intra– and intersexual selection in substrate–based groups with (1) male aggression but no courtship, (2) male courtship but no aggression, and (3) both male courtship and aggression. The final category, groups most closely resembling ‘classical’ lek species, receives most attention; data from drosophilid and tephritid fruit flies are presented to show interspecific differences in the influence of male aggression and female choice on male mating success. Few data are available that address the evolutionary origins of lek behavior in insects. Among male–initiated hypotheses, it is most likely that males cluster at transit ‘hotspots’ where large numbers of females are likely to pass. There is no empirical support for the idea that clustering increases signal effectiveness and hence female arrivals on a per male basis. In addition, data regarding predation and group size do not consistently reveal reduced risks with increasing group size.

ABSTRACT

We discuss two pivotal components of salticid mating systems. The first is complexity of behavior during salticid intraspecific interactions, characterized by conditional strategies composed of distinctly different tactics and, within the context of each tactic, large repertoires of distinctive displays combined in highly variable sequences. Variability in the display repertoire of male salticids is probably the main focus of female choice. The second is the relationship of mating strategies to predation, antipredator protection and other processes in the animal's life. During conspecific interactions, there are conflicting interests because of the potential for cannibalism, and a salticid may be a potential mate or prey and rival or predator. We suggest that during these interactions, salticids may orchestrate a careful balance between stimuli that provoke (e.g. sensory exploitation) and stimuli that inhibit predatory attacks from each other. We draw parallels between salticid intraspecific interactions and the araneophagic predatory strategy of Portia, a genus of salticids that practice aggressive mimicry. In both systems, signaling may best be envisaged as a way of achieving dynamic fine control of another animal's behavior.

INTRODUCTION

Jumping spiders (Salticidae) are the largest family of spiders (over 4000 described species (Coddington and Levi 1991)); they are well known for excellent vision (Land 1969a,b; Blest et al 1990) and elaborate visual courtship displays (Crane 1949). Our goal in this chapter is to develop a fresh perspective on salticid mating strategies.

ABSTRACT

In the leaf beetles (Coleoptera: Chrysomelidae) males and females mate with multiple partners and form prolonged associations that last for hours or even days. In some species, males exhibit elaborate courtship behaviors while riding on females' backs before, during, or after insemination. Females often respond to copulation attempts by positioning their abdomens out of reach of the male's genitalia or by kicking males with their legs. Examination of internal events suggests that females control the ability of males to fully evert their genitalia and inseminate. Females of some species also emit sperm during or after copulation. Experimental work indicates that the spermathecal muscle plays a role in sperm retention and fertilization of eggs, suggesting that females control emission and retention of the male's sperm. Comprehensive analysis of the fitness consequences of prolonged and multiple mating has not been attempted for any species in the Chrysomelidae. Although mateguarding appears to be one important function of prolonged pairing, prolonged pairing can increase proportional paternity even when it does not reduce the likelihood of remating by the female. An intriguing body of evidence suggests that cryptic female choice may occur in the leaf beetles, where females accept, retain, and use sperm of males of preferred phenotypes. The hypothesis that females exert postmating female choice by manipulating retention and use of sperm should occupy significant numbers of behavioral ecologists in the coming decade.

ABSTRACT

The three orders of Neuropterida are together considered to be the basal, most plesiomorphic representatives of the Endopterygota (= Holometabola; insects with complete metamorphosis). Therefore, their mating systems are particularly interesting from a phylogenetic perspective, in that they could provide insight into the ancient past of insect behavioral evolution. However, sexual behavior is extremely diverse within the 21 families of Neuropterida, and not unlike that found in insects that are usually considered more ‘advanced’. This chapter describes what little is known of sexual attraction, courtship and mating in the orders Megaloptera, Raphidioptera and Neuroptera. Each neurop – terid mating system shows clear signs of having been molded by the same intense and conflicting pressures of mate attraction and intersexual and intrasexual competition that have been described for other animal and plant groups. In the most plesiomorphic taxa (Sialidae, Raphidioptera, Ithonoidea), female pheromones serve to attract multiple males; this attraction has produced synchronized swarming behavior and male scramble–competition polygyny in some species. Also plesiomorphic and nearly universal within the superorder is sperm transfer by means of a large spermatophore, which can represent a significant paternal investment. Probably as a consequence, prolonged copulation and mate–guarding have evolved wherever particularly large spermatophores are exchanged. Courtship is found in the majority of Neuropterida, and is usually mediated by sex pheromones deployed by males from an anatomically diverse array of androconia (scent glands).

Sexual behavior and social behavior are profoundly alike in that both involve one set of individuals more or less willingly providing a limiting resource to another set (Queller 1994). Thus, in sexual interactions females provide resource–rich ova and other parental investment to males, and in social interactions workers provide labor to queens. In both situations, the parties are virtually always in conflict over the allocation of the resources, but their interests also partly coincide: eggs must be fertilized and offspring produced, and a new generation of reproductives must be successfully protected and reared. The complex mixtures of conflict and cooperation that thus typify sex and sociality make them among the most endlessly fascinating and difficult topics in ecology and evolution.

This book, and its companion (Choe and Crespi 1997), explore the intricacies of sexual and social competition. We have drawn together, for each of these topics, a set of authors whose expertise is both taxon–deep and broadly based in the theory that guides interpretation of natural history. Our goal has been to bring theory and observation together, to find parallels and convergences between disparate taxa, and to sketch out the patterns of engagement that will allow us to understand how conflicts and confluences of interest evolve together.

ABSTRACT

The male–female interaction is an asymmetrical, usually obligate mutualism in which there are conflicts of interest whenever multiple potential partners that vary in quality are available for either sex. Understanding male–female confluences and conflicts of interest is required to explain the sexual sequence and how it evolves. Mating interactions involve multiple steps or stages, distinguishable because of differences arising out of changes in selection that occur during the sequence. Sexual selection and competition take several different forms, which must be understood before accurate interpretations can be made of mating events in any particular case.

Sexual selection guided primarily by male–female conflicts of interest can result in resolvable evolutionary chases that lead to evolutionary stable strategies but perhaps more frequently lead to chases that tend to be unending (Parker 1979).

ABSTRACT

Pseudoscorpions are an ancient order of arachnids whose mating systems display an interesting mix of phylogenetic conservatism and evolutionary plasticity. A 400 millionyear– old pattern of indirect sperm transfer by means of spermatophores deposited on the substrate pervades all aspects of sexual selection in pseudoscorpions. Across families, mating behavior ranges from the ancestral condition, in which males deposit structurally simple spermatophores irrespective of the presence of females (non–pairing), to a derived condition in which males engage in elaborate courtship and assist females in the uptake of structurally complex spermatophores. In non–pairing taxa, sexual selection appears to be mediated through rapid male development and prolific spermatophore production. Males are invariably the smaller sex and do not fight over access to females. Why non–pairing has persisted in six of seven superfamilies remains an enigma. Cladistic analysis suggests that pair formation has evolved independently only once. Evidence from within the most diverse family, the Chernetidae, indicates that, once pair formation evolved, sexual dimorphism became a highly variable condition. Only in productive, and hence often ephemeral and patchily distributed, micro – habitats do populations reach densities at which selection for fighting ability outweighs the costs of attaining competitive size. The harlequin–beetle–riding pseudoscorpion, Cordylochernes scorpioides, has provided a model system both for assessing the influence of ecological factors on the operation of sexual selection and for identifying processes that can maintain variability in male sexually selected traits.

ABSTRACT

The mating signals and ecology of fireflies are diverse and the biology of exceptional species can be a source of historical information. Such species are functioning theoretical models and as working surrogates can be used for observational and experimental studies on the selection pressures, population divergences, and trajectories of history. Transitions between signaling modes and ecology, the impact of signal–focusing predators, and the influence of a species' unique ecology on its sexual biology are among phenomena that extant fireflies may illuminate. This paper describes idiosyncratic elements in the mating biology of several lampyrids, and then outlines some basic patterns in the mating biology of Photuris fireflies, themselves firefly predators and important agents of selection for many other fireflies.

INTRODUCTION

Fireflies initially caught my interest because they provided an opportunity to work taxonomically with a little–known group of attractive organisms, in the fashion of naturalists and curators of the past. Early observations by F. A. McDermott and H. S. Barber (1910–1951; review in Lloyd 1990) showed possibilities that existed. The renewed discussion of Darwin's sexual selection (Campbell 1972; Otte 1979), with the fresh perspectives for firefly systematics that were revealed (Lloyd 1979) and the Byzantine signal complexities and confusion of the genus Photuris and their interactions with species that occur with them, have sustained pursuit (Barber and McDermott 1951; McDermott 1967; Lloyd 1969a, 1980,1981a,b, 1984a,b, 1986, J. E. Lloyd, taxonomic monograph in preparation).

ABSTRACT

Sexual selection in resource defense polygyny systems is characterized by male–male competition for valuable resource patches, female settlement among patches based on both resource quality and male quality, and positive correlations between resource quality and male quality. These correlations confound the processes of sexual selection and pose special challenges for their study. Ligurotettix, an unusual genus of gomphocerine grasshoppers in which males defend individual host shrubs as mating territories, have proved to be useful species for investigating these issues.

Female Ligurotettix generally settle on certain host shrubs whose foliage represents high–quality food, which may promote egg development. Males are usually found on the same set of host shrubs that harbor females. The settlement of adult males, which occurs prior to the seasonal appearance of adult females, is based on the expected value of a shrub as both a female encounter site and a food resource whose consumption could increase male competitive abilities. Males compete for exclusive residence at valuable shrubs by means of early adult maturation, searching mechanisms for finding the shrubs, and aggression. Loud acoustic signaling by the males attracts females and influences their initial settlement among these shrubs.

Despite high levels of aggression, Ligurotettix males congregate on the most valuable host shrubs. Females may prefer congregated males per se, possibly as a means of reducing the costs of selecting males and locating resources. Some findings suggest that males display mutual attraction and exploit this possible female preference.

ABSTRACT

Mate–finding in the large majority of moths is mediated by a long–distance response of males to minute quantities of pheromone emitted by females. Additionally, in many species, males may produce their own pheromone, which is employed after the sexes are brought together. More rarely, males produce acoustic signals and/or a long–distance pheromone. In the latter case, females assume the searching role. The female pheromone systems of the Heteroneura, a group that makes up 99% of extant Lepidoptera, may have had a single origin with relatively little change occurring subsequently, either in the types of chemicals used or in the glandular structures for pheromone production and release. In addition, female signaling appears to be a plesiomorphic trait for the Lepidoptera that likely was lost independently several times among the primitive groups. Recent research points to the female sternum V gland (located on the fifth abdominal sternum), found throughout primitive Lepidoptera, as the most likely evolutionary predecessor of the heteroneuran sexpheromone system. This gland, which is shared with the sister group Trichoptera, also appears to play a defensive role in some species of the two orders. In contrast to the conservation of female pheromone systems, the incidence of male pheromones in moths is exceedingly polyphyletic and labile, suggesting intense and repeated selection for a transient function. Male acoustic signaling, although less prevalent, also appears to have had multiple origins.

ABSTRACT

Fig–pollinating and fig–parasitizing wasps are integral parts of one of the most fascinating plant–insect interactions known. Moreover, studies of these wasps have been instrumental in developing and refining ideas concerning the influence of population structure and inbreeding on shaping the outcome of kin selection. We present data compiled from six studies spanning five continents that relate brood sex ratios with foundress number in 24 pollinator species. All predictions of local mate competition (LMC) and inbreeding theory are at least qualitatively supported. Additionally, the sex ratios produced by single foundresses of any given species appear to be influenced by brood size and the frequency of multiple foundress broods in that species. We then consider the assumptions underlying the testing of the specific LMC model and consider the relative merits of observational and experimental tests of the theory. Furthermore, we discuss the existing studies of the parasitic wasp species that have addressed the unusual morphological and behavioral polymorphisms for flightlessness and lethal combat that are found in the males of these species. These differences appear to be influenced by the parasites' population structure and density, although other factors are also implicated. Finally, we compare the nature of the support for LMC theory from fig–pollinating wasps with that from the parasitoid wasp Nasonia vitripennis, and suggest future lines of research.

ABSTRACT

Butterflies display a variety of sexual differences in size and morphology beyond those found in the gonads and genitalia. The size and nature of such differences can be explained as (1) the result of selection pressures acting on one or both sexes that are a function of these differences, or (2) as the incidental consequence of selection acting independently on each sex. This chapter reviews various attempts to relate mating–system structure and ecology to these explanations for sexual dimorphism in butterflies. Females are usually larger than males in butterflies; although there are positive size–fecundity relationships in females, the patterns of selection on male size are not understood well enough to explain this pattern. Body and wing shape reflect male mate–locating tactics, but selection pressures shaping female wing and body shape characteristics are poorly known. Sexual selection still appears to be a likely explanation for the elaborate colorations, scent–pro – ducing, and sensory structures in males, although there is clearly more work to be done. These sexual differences all appear to be the products of selection acting independently on the sexes, whereas sexual differences in eclosion patterns might be explained by selection for specific sexual differences in eclosion dates.

INTRODUCTION

A variety of sexual differences in morphology, beyond the gonads and genitalia, are common in butterflies. These include differences in wing color, wing shape, body size, body proportions, sensory structures, foreleg development, and signal–producing structures (Fig. 15–1).

ABSTRACT

Two sympatric species of Zoraptera in central America, Zorotypus barberi Gurney and Z. gurneyi Choe, exhibit distinctively divergent mating behaviors before, during, and after copulations. The mating system of Z. barberi is essentially polygynandry in which both males and females mate with multiple mates. Males of Z. barberi perform elaborate precopulatory courtship involving courtship gifts, provide extra stimulation during copulation, and continue to court for additional copulations. Females appear to exert almost exclusive control over mating by being able to reject males at any point during the entire mating episode. In addition to deciding with whom to mate and how long each copulation lasts, Z. barberi females also control the frequency of copulations. They can mate with one male repeatedly, with different males, or both. Among the hypotheses examined, the material–benefit, postcopulatory female choice, sperm–supply, and fertilization–enhancement hypotheses, or some combinations of them, appear to provide good explanations for the observed mating variations in Z. barberi. Alternatively, repeated mating may be a result of ‘parceling’ of courtship gifts by males to guard females for a longer period of time. In Z. gurneyi, males gain considerable control over mating by establishing dominance hierarchies among themselves and thus predetermining female mating decisions to a certain degree. Zorotypus gurneyi males display no apparent precopulatory courtship; once genital coupling is made, they are able to prolong copulations by everting much of their internal genitalia into the female. After copulations, dominant Z. gurneyi males continue to protect their harems of females from other males.